[TriLUG] Negative search in Vi

[Craig Taylor]

Ack, you're right - As I said I didn't check it before posting - however
after reading the vi :help on pattern matching and trying umpteen different
ways I've found

1) Lots of confusing regexp stuff.  :-)

Something similar to /\(.|..|[^d][^o][^g].*\)/\@!  might work but I can't
get the syntax right... I may be misunderstanding the use of the \@! syntax.


To get back to the original issue -

Try this (I did test these... )

  - Replace "dog" with a symbol that's not used in your file, eg : @
  - Search for all lines that do not have an @ :   /^[^@]*$
  - After you're finished, replace @ with dog again.

- Craig Taylor

On Sat, Apr 12, 2008 at 7:09 PM, Michael Tharp <gxti at partiallystapled.com>
wrote:

> Craig Taylor wrote:
> > Negate your regular expression search, eg: for lines that don't have
> 'dog'
> > use :
> >
> > /^.*[^d][^o][^g].*$
> >
> > disclaimer: this has not been tested - I believe it should work 'tho)
> >
> > - Craig Taylor
>
>  >>> foo = re.compile('^.*([^d][^o][^g]).*$')
>  >>> sample = 'the quick brown fox jumped over the lazy dog'
>  >>> bool(foo.search(sample))
> True
>  >>> foo.search(sample).groups()
> (' do',)
>
> The problem here is this:
> 1. The first ".*" gobbles up everything up to "dog"
> 2. [^d][^o][^g] doesn't match "dog", so it backtracks by one character
> to " do"
> 3. It matches, since " do" != "dog"
> 4. The second ".*" gobbles up the remainder of the string
>
> Doing negative matches is surprisingly difficult and I honestly can't
> say I know of a way to do this with just a regular expression, either.
> Aaron's suggestion of deleting all matching lines and stepping through
> the remainder is probably the most plausible. Honestly, if this is
> possible, it has to be a feature of vim itself, not some regex trickery.
>
> As I wrote this, Kevin posted a recommendation for lookahead/behind
> assertions, but remember that those only work if you have something to
> anchor them to! You can't say "match anything but dog" with an assertion
> unless you have something that you *do* match first, and then say "match
> if it is not followed by dog". In Kevin's example, the anchor is the end
> of the string, but this is insufficient for simply checking whether
> something is not present if it could be anywhere in the middle.
>
> -- m. tharp
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